1. Field of the Invention
This invention relates generally to apparatus for handling and stacking thin flexible objects or strips, and is particularly useful with labels, tickets, cards, and the like.
2. Description of the Prior Art
There is a continuing need for improvements in methods and apparatus for handling and stacking thin flexible objects such as labels. The speed of printing machines, as both mechanisms and inks are improved, continue to increase. So, machines for handling and stacking such strips must also operate at high speeds to push articles onto a stack and operate reliably to prevent back up and interference with the continuous operation desired.
Simplicity in the use of components is therefore highly desirable. Some previous machines, such as that disclosed in U.S. Pat. No. 4,474,366, utilize a larger number of mechanical elements such as dogs or pusher feet which are satisfactory at slower speeds, but have more maintenance or shut-down problems because of the larger number of elements subject to wear and failure.
Other prior art disclosures in U.S. Pat. Nos. 4,440,388; 4,310,152 and 4,261,559 rely on internal switching of vacuum connections to drum surfaces that varies the vacuum force and/or provides compressed air to the drum surface. Again, these are complicated and expensive mechanisms that do not do as well in the long term as the apparatus described herein.
Finally, if the strips are labels, then the stack of labels should not include bent, buckled or otherwise deformed labels because the stack is to be used in direct feed operations in label application to containers. If the stack does contain such deformed labels then the label application machinery may jam, shutting down the operation of not only the application station but also the entire bottling or container filling line.
While the present invention is useful for handling labels made from all materials, it is particularly useful with labels made from thermoplastic materials such as expanded oriented polystyrene or cellular polymeric materials. Labels made from such materials sometimes tend to warp or cup making them more difficult to handle in general and particularly difficult to stack with existing apparatus.